Vacuum arc deposition apparatus

Abstract: A vacuum arc deposition apparatus includes arc power sources having cathodes connected to both ends of an evaporation source; exciting coils disposed at positions axially outwardly far from both the ends of the evaporation source so as to be coaxial with the evaporation source; and coil power sources independently connected to the exciting coils. In this apparatus, each of the coil power sources is capable of controlling the exciting current in such a manner that the film thickness and the consumption of the evaporation source are suitably distributed. Moreover, an arc containment device of the vacuum arc deposition apparatus includes an arc containment body having a diameter substantially the same as that of a cylindrical evaporation source, which is disposed at one end portion of the evaporation source.

Description: The present invention relates to a vacuum arc deposition apparatus for forming a film on a workpiece using vacuum arc discharge. Of methods of forming films in vacuum, a vacuum arc deposition method capable of effectively forming a film has been widely used in industrial applications. The vacuum arc deposition method includes the steps of generating the so-called vacuum cathode arc discharge between a cathode and an anode disposed in a vacuum vessel, evaporating the material of the cathode from arc spots generated on the surface of the solid cathode, and depositing the vapor of the evaporated material on a substrate disposed in the vacuum vessel thereby forming a film. Apparatuses for carrying out the vacuum arc deposition method have been known, for example in Unexamined Japanese Patent Publication No. HEI 5-106025 (EP-A-0 508 612). The above-described prior art method is characterized by providing an axial magnetic field formed on the surface of the evaporation source (this is formed by a spiral coil disposed around the rod-like evaporation source) and a circumferential magnetic field formed at least partially on the surface of the evaporation source (this is excited by an arc current flowing in the rod-like evaporation source), wherein the velocity and the direction of arc spots are controlled by the combination of these two magnetic fields. Of various examples disclosed in the above-described document, there is shown the example of supplying arc currents from both ends of the arc evaporation source. This example is intended to perform a substantially continuous discharge from the rod-like evaporation source. According to this document, it becomes possible to continuously realize uniform discharge in the axial direction by reciprocating arc spots along the axial direction of the evaporation source using the balanced currents supplied from both the ends of the evaporation source. In the above document, there is further disclosed a technique of providing sensors for detecting arc spots at both the ends of the evaporation source (target), thereby exactly controlling the reciprocating movement of arc spots on the basis of signals from the sensors, resulting in the uniform consumption of the target. The prior art technique of providing the sensors, however, has arisen a problem in that the control of arc spots by signals from the sensors is complicated and requires an expensive controller with a complex structure. Notwithstanding such a complex controller, it has been difficult to prevent the localization of arc spots at the end portions of the target because of an increase in arc discharge current and of extension in the target length. As for the control of arc spots by adjustment in the cathode current balance, it is effective for the case that the total current is small; however, in the case where the total current is increased, the scanning of arc spots is difficult or the scanning direction of arc spots is reversed even by increasing the difference in currents at both the ends, thus largely deteriorating the controllability. Additionally, in the apparatus having an arc containment ring ("insulator 12" in the above-described document) provided at each end portion of the cylindrical evaporation source for preventing the escape of arc spots from the specified evaporating surface of the cylindrical evaporation source, there occurs the following problem. Namely, the arc containment ring has an outside diameter sufficiently larger than that of the cylindrical evaporation source and is coaxially inserted around the end portion of the cylindrical source, so that when the arc discharge is continued for a long time on the surface of the cylindrical evaporation source, the vapor of the evaporated material is deposited on the surface of the arc containment ring projecting outwardly from the evaporating surface, and the deposited material on the surface of the ring is short-circuited with the evaporation source, thereby making insufficient the arc containment function. SUMMARY OF THE INVENTION An object of the present invention is to provide a vacuum arc deposition apparatus capable of preventing the shifting of arc spots to the end portions of an evaporation source without any complex control, thereby realizing the uniform film thickness distribution and preventing local consumption of the evaporation source. To achieve the above object, according to a first aspect of the present invention, there is provided a vacuum arc deposition apparatus in which a cathode of an arc power source is connected to an end portion of a cylindrical evaporation source, comprising: magnetic field forming means provided at positions axially outside of both end portions of the evaporation source in such a manner as to be coaxial with the evaporation source. With this construction, it becomes possible to prevent the localization of arc spots to the end portions of the evaporation source, and hence to suppress the local consumption of the target liable to be generated at the end portions. Specifically, as shown in Fig. 8, when magnetic field forming means 8 is disposed at a position axially outwardly far from the end portion of an evaporation source 2 in such a manner as to be coaxial with the evaporation source 2, a magnetic field is formed near the end portion of the cylindrical evaporation source 2. The lines of magnetic force formed by the magnetic field forming means 8 are largely focussed in the interior of the magnetic field forming means 8 and are diverged at positions separated from the means 8. Accordingly, the lines of the magnetic force show the configuration passing through the evaporation surface outwardly from the inner side in the direction from the end portion to the center portion of the evaporation source 2. As shown in Fig. 9, when the evaporating surface of the evaporation source 2 intersects the lines of the magnetic force, the vacuum arc spot receives a first force in the circumferential direction of the evaporating surface due to the interaction between the lines of magnetic force and arc current, and a second force in the direction where the intersecting angle between the evaporation source 2 and the lines of magnetic force becomes acute. The first force only gives the turning motion on the target to arc spots; but the second force exhibits a function of shifting arc spots from the end portion to the center portion of the evaporating surface of the evaporation source 2. As described above, in the case where a cylindrical evaporation source is continuously discharged using a large current, arc spots tend to be shifted to the end portion of the evaporation source; however, as shown in the present invention, the use of the above second force can cancel the shift of arc spots, and can eliminate the target consumption shifted to the end portion and uneven film thickness distribution. In the above apparatus, the magnetic field forming means may be composed of an exciting (or: excitation) coil, and a coil power source, which is provided for supplying an exciting current to the exciting coil, is preferably capable of controlling the exciting current in such a manner that the film thickness and the consumption of the evaporation source are suitably distributed. With this construction, since the exciting current to the exciting coil can be controlled, it becomes possible to suitably control the intensity of the magnetic field and hence to realize the uniform consumption of the target and the uniform film thickness distribution. The magnetic field forming means may be axially movable. With this construction, it becomes possible to suitably control the intensity of the magnetic field applied to the evaporation source, and hence to realize the uniform consumption of the target and the uniform film thickness distribution. A plurality of the magnetic field forming means may be provided, each of which is capable of controlling the intensity of the formed magnetic field. With this construction, it becomes possible to suitably control the intensity of the magnetic field applied to the evaporation source, and hence to realize the uniform consumption of the target and the uniform film thickness distribution. According to a second aspect of the present invention, there is provided a vacuum arc deposition apparatus comprising: arc power sources, cathodes of which are connected to both ends of an evaporation source; exciting (or: excitation) coils disposed at positions axially outside of both the ends of the evaporation source in such a manner as to be coaxial with the evaporation source; and coil power sources independently connected to the exciting coils; wherein each of the coil power sources is capable of controlling the exciting current in such a manner that the film thickness and the consumption of the evaporation source are suitably distributed. With this construction, since the exciting coils are each disposed at both the ends of the evaporation source, arc spots are shifted from both the ends to the inner side of the evaporation source, thus preventing the localized target consumption and the uneven film thickness distribution at both the ends. The arc power source may share the coil power source. With this construction, the structure of the apparatus can be extremely simplified. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing the construction of a first embodiment of the present invention; Fig. 2 is a graph for explaining the function of the first embodiment; Fig. 3 is a graph for explaining the function of the first embodiment; Fig. 4 is a graph for explaining the function of the first embodiment; Fig. 5 is a schematic view showing the construction of a modification of the first embodiment of the present invention; Fig. 6 is a schematic view showing the construction of another modification of the first embodiment of the present invention; Fig. 7 is a schematic view showing the construction of a further modification of the first embodiment of the present invention; Fig. 8 is a schematic view for explaining the function of the present invention; Fig. 9 is a schematic view for explaining the function of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic view showing the whole construction of a vacuum arc deposition apparatus, wherein a cylindrical deposition source 2 is disposed in a vacuum vessel 1. Both the ends of the evaporation source 2 are each electrically connected to and held by holders 4. The holders 4 are supported in the right and left side walls of the vacuum vessel 1 by way of insulators 3. An arc containment ring 5 for covering the boundary portion between each holder 4 and the evaporation source 2 is provided around the outer peripheral area of the holder 4. A substrate 6 as a workpiece is disposed to surround the evaporation source 2. With respect to the evaporation source 2, at least the outermost peripheral portion thereof is made of a material to be evaporated and to form a film on the substrate 6. The evaporation source 2 is called a target. Cathodes of arc power sources 7 are respectively connected to the right and left holders. Anodes of the arc power sources 7 are connected to the vacuum vessel 1. In this embodiment, the vacuum vessel 1 itself is taken as an anode; however, an independent anode electrode may be disposed in the vacuum vessel 1, as needed. A pair of the right and left arc power sources 7 corresponding to the right and left holders 4 are provided. Magnetic field forming means 8 are each provided at positions axially outwardly far from both the ends of the evaporation source 2. The magnetic field forming means 8 are composed of cylindrical exciting coils. The exciting coils 8 are disposed to be coaxial with the evaporation source 2. In this embodiment, the exciting coils 8 are disposed outside the vacuum vessel 1. The exciting coils are independently connected to coil power sources 9. The coil power source 9 is capable of controlling the exciting current applied to each exciting coil 8. A striker 10 of an ignition device is provided on the inner surface of the vacuum vessel 1. The vacuum vessel 1 can be kept at a specified pressure by an exhaust device (not shown). To form a film on the substrate 6 by the vacuum arc deposition apparatus, the interior of the vacuum vessel 1 is kept at a vacuum state with a specified pressure by evacuation using the exhaust device (not shown), and vacuum arc discharge is generated from the evaporation source 2 by the striker 10. With this vacuum arc discharge, arc spots where arc current is concentrated appear on the surface of the evaporation source 2, which evaporate the evaporation source material (target material). The vapor of the evaporated target material is moved toward the substrate 6 disposed in the vacuum vessel 1, to form a film on the substrate 6. The substrate 6 may be applied with a negative voltage (bias voltage) by a power source (not shown) as needed, and in this case, the film formation is performed while ions in the vapor is accelerated. A reactive gas such as nitrogen may be introduced in the vacuum vessel 1 as needed for forming a film of a compound with the target material. In the film formation, the arc spot generated on the surface of the evaporation source 2 is reciprocated from the one axial end to the other axial end of the evaporation source 2, to control the target material to be uniformly evaporated from the surface of the evaporation source 2. This control of evaporation will be described below. In this embodiment, there is used the evaporation source 2 having the length of 800 mm and the diameter of 90 mm; and the exciting coil 8 having a diameter of 315 mm at the center position of the winding is disposed at the position separated from the evaporation source 2 by 200 mm. Prior to the description of the control of evaporation in this embodiment, a comparative example in which no current is applied to the exciting coil 8 will be described. The comparative example was performed as follows: namely, in the state that no current was applied to the exciting coils 8, vacuum arc discharge was generated by supplying a total current of 1000 A (each current: 500 A) from both the ends of the evaporation source 2 by the arc power sources 7. As a result, it was visually observed that arc spots were liable to be shifted to the end portions of the evaporation source 2. In such a state, the discharge was performed for 4 hr in total. Consequently, both the ends of the evaporation source 2 were consumed by evaporation and constricted in a level visible to the naked eye; and as shown by the film thickness distribution in the curve (a) of Fig. 2, the film formation rate was particularly high at both the ends of the substrate 6. On the other hand, according to this embodiment, the same discharge as in the above comparative example was generated from the surface of the evaporation source 2 in the state that the exciting coils 8 at both the ends of the evaporation source 2 were each excited at 5000 AT by the coil power sources 9. As a result, it was visually observed that arc spots were collected at the central portion of the evaporation source 2. The arc spots near the end portion of the evaporation source 2 were turned in a spiral shape by the effect of the axial component of the magnetic field generated by the exciting coil 8. On the contrary, the arc spots at the center portion of the evaporation source 2 were moved in a random fashion by no effect of the magnetic field generated by the exciting coil 8. As for the exciting directions of the coils 8 at both the ends of the evaporation source 2, the function of shifting arc spots to the center portion of the evaporation source 2 is not changed in either case that the exciting directions are the same or reversed to each other, which shows that either polarity is usable. Even by the discharge for about 20 hr in such a state, the consumption of the end portions of the evaporation source 2 was not observed so much. In such a state, the film formation test on the substrate 6 was carried out in the same manner as in the comparative example, which gave the film formation distribution shown by the curve (b) of Fig. 2. As is apparent from this film thickness distribution, the film formation rate near the center portion of the evaporation source 2 is increased. The same film formation test was performed except that the exciting current of the exciting coil 8 was set at 2000 AT, which gave the film formation distribution shown by the curve (c) of Fig. 2. As is apparent from this film formation distribution, the film formation rate is nearly uniform substantially over the whole length of the evaporation source 2. This shows that the uniform film thickness distribution can be easily obtained by suitably adjusting the current of the exciting coil 8. As described above, according to this embodiment, it becomes possible to solve the prior art problem of shifting arc spots to both the ends of the long cylindrical evaporation source upon a large current discharge and hence to suppress the consumption of the end portions of the evaporation source, which leads to the good film thickness distribution in the axial direction of the target. In addition to the uniform film thickness distribution, there can be adjusted the film thickness distribution by the control of currents of the exciting coils 8 at both the ends of the evaporation source 2. For example, by increasing the coil current I1 of one exciting coil 8 more than the coil current I2 of the other exciting coil 8, arc spots can be shifted to the side where the exciting current is small, thus adjusting the film thickness distribution. A further uniform film thickness distribution can be obtained by changing the current I 1 and I 2 of the exciting coils with time, as shown in Fig. 4. For example, the film thickness distribution shifted to the center portion and the distribution shifted to the end portion are alternately generated by periodically repeating the magnitude of the supply current to the exciting coil 8, and by composition of these two film thickness distribution, the uniform film thickness distribution and the uniform target consumption can be realized. Fig. 5 shows a modification of the first embodiment of the present invention, wherein each of the exciting coils at both the ends of the evaporation source 2 is divided into a plurality of parts for selectively using each coil 8. Specifically, the exciting coil 8 is divided into an inner coil 8a and outer coil 8b disposed to be coaxial with each other. The inner and outer coils 8a and 8b are respectively connected to the power sources 9a and 9b such that the supply currents thereto can be independently controlled. The diameter of the exciting coil 8 and the distance between the exciting coil 8 and the end portion of the evaporation source 2 exert an effect on the configuration of the magnetic field generated by the coil 8, which in turn exerts an effect on arc spots. For example, when the diameter of the exciting coil 8 is small, the effect exerted on the position separated from the coil 8 is significantly reduced, that is, the effect of the magnetic field generated by the coil 8 is limited to the vicinity of the coil 8. Accordingly, in the case where the function of the coil 8 is limited to the prevention of the local consumption of the end portion of the evaporation source 2, the diameter of the coil 8 may be set to be smaller. On the contrary, in the case where the effect of the magnetic field is desirable to be exerted even to arc spots far from the end portion of the evaporation source 2, the coil 8a having a small diameter and the coil 8b having a large diameter are combined, and by the combination of the exciting currents, the effect exerted on the arc spots can be controlled. Fig. 6 shows another modification of the first embodiment of the present invention, wherein the position of the exciting coil 8 is variable. Specifically, the exciting coil 8 is provided to be movable in the axial direction, so that the intensity of the magnetic field generated by the coil 8 against the evaporation source 2 can be adjusted by controlling the position of the coil 8 using a moving device (not shown). With this construction, the degree of the function applied to arc spots becomes variable. Fig. 7 shows a further modification of the first embodiment of the present invention. As is apparent from this figure, it is effective in terms of economy that at least part of the exciting current of each of the exciting coils 8 at both the ends is supplied from the arc discharge current itself by a power source 11 for common use in the arc power source and the coil power source. The present invention is not limited to the above embodiment and the modifications. For example, the magnetic field forming means is not limited to the exciting coil, but may include the other devices of forming a magnetic field diverged outwardly from the center line in the direction from the end portion to the center of the evaporation source. Moreover, the magnetic field forming means may be provided in the vacuum vessel, and only at one end portion of the evaporation source. Additionally, a pole piece made of a magnetic body for effectively introducing the magnetic field formed by the exciting coil to the end portion of the evaporation source may be provided at the portion ranging from the interior of the coil to the vicinity of the end portion of the evaporation source.

Claims: A vacuum arc deposition apparatus in which a cathode of an arc power source (7) is connected to an end portion of a cylindrical evaporation source (2), comprising: magnetic field forming means (8) provided at positions axially outside of both end portions of said evaporation source (2) in such a manner as to be coaxial with said evaporation source (2). A vacuum arc deposition apparatus according to claim 1, wherein said magnetic field forming means (8) comprises an exciting coil, and a coil power source (9), which is provided for supplying an exciting current to said exciting coil (8), is capable of controlling the exciting current in such a manner that the film thickness and the consumption of said evaporation source are suitably distributed. A vacuum arc deposition apparatus according to claim 1, wherein said magnetic field forming means (8) is axially movable. A vacuum arc deposition apparatus according to claim 1, wherein a plurality of said magnetic field forming means are provided, each of which is capable of controlling the intensity of the formed magnetic field. A vacuum arc deposition apparatus comprising: arc power sources (7), cathodes of which are connected to both ends of an evaporation source (2); exciting coils (8) disposed at positions axially outside of both the ends of said evaporation source (2) in such a manner as to be coaxial with said evaporation source (2); and coil power sources (9) independently connected to said exciting soils (8); wherein each of said coil power sources (9) is capable of controlling the exciting current in such a manner that the film thickness and the consumption of said evaporation source (2) are suitably distributed. A vacuum arc deposition apparatus according to claim 5, wherein said arc power source shares said coil power source.

Inventors: FUJII HIROFUMI, HANAGURI KOJI, KAWAGUCHI HIROSHI, SHIMOJIMA KATSUHIKO, SUZUKI TAKESHI, TAMAGAKI HIROSHI, FUJII, HIROFUMI, HANAGURI, KOJI, KAWAGUCHI, HIROSHI, SHIMOJIMA, KATSUHIKO, SUZUKI, TAKESHI, TAMAGAKI, HIROSHI, FUJII, HIROFUMI, C/O TAKASAGO WORKS IN, HANAGURI, KOJI C/O TAKASAGO WORKS IN, KAWAGUCHI, HIROSHI, C/O TAKASAGO WORKS IN, SHIMOJIMA, KATSUHIKO, C/O TAKASAGO WORKS IN, SUZUKI, TAKESHI C/O TAKASAGO WORKS IN, TAMAGAKI, HIROSHI, C/O TAKASAGO WORKS IN
Applicants: KOBE STEEL LTD, KABUSHIKI KAISHA KOBE SEIKO SHO ALSO KNOWN AS KOBE STEEL LTD.
Application year: 1994
Main classification: C23C14
IPC codes: H01J37, C23C14